1. Field of the Invention
The present invention relates, in its broadest aspect, to industrial ice making machines, which means machines that are generally used for professional reasons, such as in public places (bars, restaurants and the like) for making ice with desired shapes and dimensions.
According to a more specific aspect, the present invention relates to ice making machines by extrusion through a die or draw plate.
2. Present State of the Art
As it is known, the shape that can be taken by the ice depends on applications and it can change from the usual cubes used for beverages, to more complex shapes such as nuggets, flakes or granules of ice; in this latter case it is mainly used for keeping food in the cool condition, such as fish or meat of refrigerated display boxes of supermarkets or restaurants.
In order to obtain such shapes and sizes of the product it is known to feed (that is to extrude) the ice through a die or draw plate, namely a suitably shaped body with channels, wherein the frozen mass coming from the evaporator is pushed by means of a mechanism that usually is an auger.
To this end such machines usually have an evaporator with a vertical axis where the water is lifted therein by a rotating auger within a main drum, that is cooled on the outside by the refrigerant; as the water is lifted in the main barrel, it gets cold and it tends to form the ice on the inner wall, which is then pushed towards the extrusion die arranged in the upper part of the evaporator.
The ice passes through the extrusion die or draw plate in the longitudinal direction forming rods, that are then crushed downstream of it by a dedicated device, thereby obtaining granules, flakes or other shapes and sizes of ice, depending on the characteristics of the rod-breaking device.
An example of an ice making machine made according to such principles, is known from the European patent application N. 495513 to Hoshizaki Denki. In this machine, as generally in all machines for making extruded ice, the critical member is the die or draw plate through which the ice formed within the main drum of the evaporator is pushed: the die has to compress the ice passing therethrough, conveying it then towards the rod-breaking device.
Therefore it is subjected to non negligible axial and tangential forces due to the ice being pushed therethrough and moreover, due to the fact that it is in communication upstream with the coldest area of the machine and downstream with the ice collecting tray that exchanges heat with the outer environment, it is subjected to thermal differences that can lead to stresses on the die and on the mouting means (bearings, bushings, etc.) inside the machine.
With reference to the above it has to be noted that the die is usually fastened to the upper part of the main barrel of the evaporator via radial dowels or screws, which penetrate therefore through its wall and are screwed at some teeth of the die, that to this end are provided with suitable threaded holes or seats.
It can be understood how holes for the fastening dowels or screws passing through the main barrel of the evaporator, weaken the structure thereof and are also possible points for the leakage of liquids; moreover, due to the fact that the screws have a different deformation with respect to the main drum of the evaporator, differential deformations can arise between them, thereby inducing such forces to make the fastening of the die as unstable, possibly causing also the screws or the thread thereof to be broken or however damaged.
It is most likely for such reason that in the above mentioned patent application the fastening screws engage into recesses provided along some teeth of the extrusion die: the thermal deformations, by means of such solution, can be compensated by clearances occurring between the screws and the aforesaid seats.
However, such a solution is not appropriate as it does not effectively help in axially stabilizing the die that, as described hereinbefore, is subjected to axial and tangential thrusts due to the forward motion of the produced ice from the auger.
Further, as it will be better explained below, the radial fastening of the extrusion die does not facilitate the operations for the maintenance of the ice making machine, which require the die to be removed in order to have access to the interior of the evaporator.